1. Field of the Invention
The present invention relates to a respiratory component measurement system, and, in particular, to a respiratory component measurement system that includes the ability to detect an orientation related characteristic, a motion related characteristic, or both of an airway adapter used in such a system and communicate one or more these characteristics with an indicating element.
2. Description of the Related Art
Respiratory component sensors, which include, but are not limited to, gas constituent sensors and gas flow sensors, are widely used and may be found in monitoring devices and therapeutic devices, such as ventilators and pressure support systems, such as CPAP machines.
Respiratory gas measurement systems typically comprise gas sensing, measurement, processing, communication, and display functions. They are considered to be either diverting, which is also referred to as a sidestream gas measurement system, or non-diverting, which is referred to as a mainstream gas measurement system. A diverting (sidestream) gas measurement system transports a portion of the sampled gases from the sampling site, which is typically an airway adapter in a breathing circuit or the patient's airway, through a sampling tube, to the gas sensor where the constituents of the gas are measured. A non-diverting (mainstream) gas measurement system does not transport gas away from the breathing circuit or airway, but measures the gas constituents passing through the airway adapter. An example of a mainstream gas airway adapter is shown in U.S. Pat. No. 5,693,944, and an example of a sidestream gas sampling airway adapter is shown in U.S. Pat. No. 6,935,338.
Conventional mainstream gas measurement systems include gas sensing/measurement components and signal processing required to convert the detected or measured signal, i.e., voltage, into a value, such as transmittance, that may be used by a host system to output a gas constituent measurement. In a mainstream gas measurement system, the gas sensing/measurement components are coupled to a sample cell, which is usually integrated with the airway adapter or is considered part of the airway adapter. The airway adapter is placed in series in the breathing circuit so that gas flowing in the breathing circuit also flow through the airway adapter.
In either a mainstream or sidestream gas measurement system, the gas sensing/measurement components are those required to output a signal corresponding to a property of the gas being measured. This signal is typically provided to a processor that converts the signal to a gas constituent measurement. The processor may be located in the same housing as the gas sensing/measurement components or may be located remote from the gas sensing/measurement components. In the latter case, a communication link is provided to provide that signal produced by the gas sensing/measurement components to the processor.
In a mainstream gas measurement system, placement of the sample cell, and hence the gas sensing/measurement components, directly in series in the breathing circuit results in a “crisp” waveform that reflects in real-time the partial pressure of the measured gas, such as carbon dioxide or oxygen, within the airway. The sample cell being located in the respiratory gas stream also obviates the need for gas sampling and scavenging, which is required in a sidestream gas measurement system.
Gas flow measurement systems measure the rate of flow of gas. Such flow measurement systems have utilized a variety of different technologies to meet the demanding requirements of the clinical and practical environments in which they are used. Among the flow measurement approaches that have been used for on-airway monitoring are:
1) Differential Pressure—measures the pressure drop or pressure differential across a resistance to flow;
2) Spinning Vane—counts the revolutions of a vane placed in the flow path
3) Hot Wire Anemometer—measures the cooling of a heated wire due to airflow passing around the wire;
4) Ultrasonic Doppler—measures the frequency shift of an ultrasonic beam as it passes through the flowing gas;
5) Vortex Shedding—counts the number of vortices that are shed as the gas flows past a strut placed in the flow stream; and
6) Time of Flight—measures the arrival time of an impulse of sound or heat created upstream to a sensor placed downstream.
With each of the different gas flow measurement approaches, the physical layout or configuration of the airway adapter requirements vary. For example, for performing a differential pressure measurement, two pressure sensing ports are typically placed across a flow restriction, also known as a flow element, so that the pressure drop across the flow element may be measured. An example of a differential pressure flow airway adapter is shown in U.S. Pat. No. 5,535,633. For ultrasonic flow measurement approaches, two windows are placed in the airway adapter, so that the ultrasonics beam interrogate the flow in an acute angle as possible with the direction of flow.
It should also be noted that airway adapters that combine different measurements, such as flow and gas measurements, in a single component are also available. Examples of an airway adapter that include the combination of a mainstream gas measurement system and a flow measurement system are shown in U.S. Pat. No. 6,312,389 and U.S. patent application Ser. No. 09/841,451 (publication no. 2002/0029003A1). The contents of which are incorporated herein by reference. An example of a combination mainstream flow sensor and a sidestream gas sampling airway adapter is shown in U.S. Pat. No. 5,088,332. The content of which is also incorporated herein by reference.
Ensuring that such sensors operate properly and produce a reliable output is of importance given that such sensors are used to monitor a physiological condition of a patient. To this end, it is known to protect against the accumulation of material, such as condensation, water, and sputum, on the measurement components, such as the windows used for IR gas measurements, film used for luminescence sensing based gas measurements, flow sensing components, diaphragms for pressure measurements, wire filaments for thermal measurements, and windows for optical or ultrasonic measurements. For example, filters have used to remove moisture and particulates from the flow of gas being delivered to the measurement components. In other situations, the measurement components are configured to be relatively robust so that they function adequately even in the presence of such materials.